How to change the size of tool previews in Gimp 2.0?

I am learning how to use Gimp 2.0, and being a former (chemical) darkroom
enthusiast, I am playing with obtaining b/w images from color ones.

The problem I encounter is that the "Channel Mixer" dialog shows a preview
of the resulting image that is very small - too small to have a clear
idea of the result. How can I change the size of that preview? I tried
with the "preferences" menu, changing the "Interface"/"Previews" item, but
it had no effect.If this matters, I am using the following version of Gimp: 2.0.4-1
(Debian).

How to change the size of tool previews in Gimp 2.0?

I am learning how to use Gimp 2.0, and being a former (chemical) darkroom
enthusiast, I am playing with obtaining b/w images from color ones.

The problem I encounter is that the "Channel Mixer" dialog shows a preview
of the resulting image that is very small - too small to have a clear
idea of the result. How can I change the size of that preview? I tried
with the "preferences" menu, changing the "Interface"/"Previews" item, but
it had no effect.If this matters, I am using the following version of Gimp: 2.0.4-1
(Debian).

well, it is not an official thing, no changelog entry count or anything
like that, just what i read from the developers interaction -- there are
great plans and such being worked on right now for all of the previews.

not only are new previews showing up in dialogs all the time (i use
gimp-2.1 from cvs) but the plans that are bantered back and forth should
make (for once) a beautiful preview interface that can be used by all of
the plug-ins.